An empty 32-foot motorboat was found floating off the coast north of Malibu Wednesday in what federal authorities said may have been used to smuggle illegal immigrants, drugs or both into California.

A passerby saw the boat -- unoccupied and unattended -- drifting off the coast just north of unincorporated Malibu and over the Ventura County line about 7 a.m. and called authorities, said David Wales, agent in charge of Immigration and Customs Enforcement-Homeland Security Investigations in Ventura County.

Inside the craft, which had two outboard motors and multiple gas cans, authorities found life preservers, backpacks and other belongings. Wales said agents were investigating whether or not the craft was "used for illicit purposes."

"We are actively investigating the case to try to make a determination whether it was human cargo or illicit substances or some combination of both, which is a possibility," Wales said.

He urged members of the public to call authorities if they see suspicious activity on the water or coast, including people coming off small craft carrying trundles or backpacks and entering waiting vehicles.

Last year, 867 illegal immigrants and smugglers were arrested at sea or along the California coast, more than double the number in 2009. Most land on San Diego-area beaches but also have been reported in Orange County including near the San Onofre nuclear power plant and Crystal Cove near Newport Beach.

Those engaging in human trafficking have also been smuggling drugs, which has led to discoveries of vessels on Catalina Island and Santa Rosa Island, off the Santa Barbara coast. Smuggling groups have also resorted to posting lookouts to watch the agents and direct boats to unmonitored areas.